1. Field of the Invention
The present invention relates generally to polyimides. It relates particularly to novel polyimides prepared from 2,3,3′,4′-biphenyltetracarboxylic dianhydride and aromatic diamines.
2. Description of the Related Art
Since 1960, more attention has focused on polyimides than any other high performance/high temperature polymers. This is due primarily to the availability of polyimide monomers (particularly aromatic dianhydrides and diamines), the ease of polymer synthesis, and their unique combination of physical and mechanical properties. A significant amount of technology has been developed such that polyimides have found wide spread commercial use as adhesives, coatings, composite matrices, fibers, films, foams, membranes and moldings. Although there are many different synthetic routes to polyimides, the most popular is the reaction of an aromatic dianhydride with an aromatic diamine to form a soluble precursor polyamide acid (amic acid) that is subsequently chemically or thermally converted to the polyimide.
Over the years a tremendous amount of work has been performed on structure/property relationships in polyimides to obtain fundamental information that could be used to develop polyimides with unique combination of properties for demanding applications. More recently, nanoparticles (e.g. clays, carbon nanotubes, inorganic nanoparticles, etc.) have been incorporated within polyimides to enhance certain mechanical and physical properties.
The National Aeronautics and Space Administration has several space applications that currently use or are evaluating polyimides. These include thin films as membranes on antennas, concentrators, coatings on second-surface mirrors, solar sails, sunshades, thermal/optical coatings and multi-layer thermal insulation (MLI) blanket materials. Depending upon the application, the film will require a unique combination of properties. These may include atomic oxygen resistance, UV and VUV resistance, low color/low solar absorption, electron and proton resistance, tear/wrinkle resistance for packaging and deployment, and high mechanical properties (strength, modulus and toughness). Atomic oxygen resistance coupled with low color and UV stability has been introduced into polyimides by using phenylphosphine oxide containing monomers.
A significant amount of work has concentrated on the polyimide from the reaction of pyromellitic dianhydride and 4,4′-oxydianiline. Several products are based upon this polymer [poly(4,4′-oxydiphenylenepyromellitimide)] such as Pyre ML® wire enamel [I. S. T. (MA) Corporation], commercial films (Kapton® produced by Du Pont and Apical® produced by Kaneka) and a Du Pont molded product, Vespel®. Another well-known film made via a polyamide acid from the reaction of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) and 1,4-phenylenediamine is Upilex® S produced by Ube Industries, Ltd.
Despite all of the known polyimides with good properties, there exists a need for a novel polyimide having low color, good solubility, high thermal emissivity, low solar absorptivity and high tensile properties.
It is therefore a primary object of the present invention to provide novel polyimides with excellent properties.
It is another object of the present invention to provide novel polyimides made from 2,3,3′,4′-biphenyltetracarboxylic dianhydride and aromatic diamines.
It is yet another object of the present invention to provide novel polyimides having low color, good solubility, high thermal emissivity, low solar absorptivity and high tensile properties.
It is a further object of the present invention to provide novel polyimides suitable for thin films as membranes on antennas, concentrators, coatings on second-surface mirrors, solar sails, sunshades, thermal/optical coatings and MLI blanket materials.